Reproductive Effects

No studies were located regarding reproductive effects in humans after oral exposure to boron.

Animal studies demonstrated that boron can cause injury after intermediate and chronic exposure to the gonads in animals, especially the testes. Impaired spermatogenesis has been reported in rats administered 300 mg/boron/L as borax (44.7 mg boron/kg/day) in drinking water for 70 days (Seal and Weeth 1980), but no reproductive effects were evident in rats administered up to 6 mg boron/L of borax (0.6 mg boron/kg/day) in drinking water for 90 days (Dixon et al. 1976). While severe testicular atrophy was seen in dogs fed up to 44 mg boron/kg/day (1,750 ppm boron, as borax or boric acid) for 90 days (Weir and Fisher 1972), partial testicular atrophy in rats occurred at a dose of 26 mg boron/kg/day (525 ppm boron) (Weir and Fisher 1972). Degeneration or atrophy of the seminiferous tubules was demonstrated in mice fed 144 mg boron/kg/day as boric acid (5,000 ppm boric acid) (NTP 1987). In rats fed at least 50 mg boron/kg/day (as borax) up to 60 days, there were reduced testicular weight and germinal aplasia at 60 days (Dixon et al. 1979). In the same study, >50 mg boron/kg/day caused reduction in hyaluronidase, sorbitol dehydrogenase, and lactic acid dehydrogenase (isoenzyme-X) at 30 days and testicular and epididymal weights were reduced (Dixon et al. 1979).

In contrast, Lee et al. (1978) did not find significant adverse effects in male rats fed 50 mg boron/kg/day (as borax) for 30 and 60 days. Dogs were fed 29 mg boron/kg/day as borax and boric acid (1,170 ppm), respectively in the diet for 38 weeks (Weir and Fisher 1972). Testicular atrophy and spermatogenic arrest were reported. When dogs were administered 8.8 mg boron/kg/day (350 ppm borax or boric acid) for 2 years, no reproductive effects were observed (Weir and Fisher 1972). Reproductive effects were reported in rats following chronic exposure. In rats fed up to 58.5 mg boron/kg/day (as borax or boric acid) for several generations, there was a lack of viable sperm in atrophied testes and ovulation decreased in females (Weir and Fisher 1972). There were testicular atrophy and interstitial hyperplasia in mice that consumed lethal doses (48 and 96 mg boron/kg/day) over a period of 103 weeks. However, the authors did not specify cause of death (NTP 1987). In a 2-generation reproduction mouse study using continuous breeding protocol, there was degeneration of the seminiferous tubules and spermatogenesis was impaired at dose levels of 111 mg boron/kg/day (636 mg/kg/day boric acid) or greater. No effects were observed in the 27 mg boron/kg/day (152 mg/kg/day boric acid) dose group (NIEHS 1990).

The highest NOAEL values and all reliable LOAEL values for reproductive effects in animals and duration category are recorded in Table 2-2 and plotted in Figure 2-2.